Alkali metal salts, molten salts, electrolytes, and secondary batteries

Abstract

We provide low-melting-point alkali metal salts X and Y. [Solution] In the embodiment, the alkali metal salts X and Y have two or more ether chains arranged in series on the opposite side of the trifluoromethylsulfonyl group, with a nitrogen atom in between. The alkali metal salt is preferably an alkali metal salt represented by formula (1). In the embodiment, the alkali metal salt has two or more ether chains arranged in series on the opposite side of the trifluoromethylsulfonyl group or fluorosulfonyl group, with a nitrogen atom in between. TIFF2026082789000034.tif19170 [In formula (1), R 1 is a trifluoromethylsulfonyl group, R 2 [-CH2-CH2-O-] is a linear organic group having two [-CH2-CH2-O-] groups, and M is an alkali metal.

Description

[Technical Field]

[0001] Embodiments of the present invention relate to alkali metal salts, molten salts, electrolytes, and secondary batteries. [Background technology]

[0002] Electric vehicles, which do not emit greenhouse gases during operation, are attracting attention as a means of realizing a decarbonized society. However, the lithium-ion batteries used in electric vehicles have a lower energy density compared to fossil fuels, resulting in a shorter driving range than gasoline-powered vehicles, which is one reason why electric vehicles have not become widespread. In addition, the electrolyte used in lithium secondary batteries is a flammable organic solvent. Flame-retardant electrolytes are needed to improve safety.

[0003] Alkali metal molten salts, being ionic liquids, do not contain solvents, making them flame-retardant and giving them a low vapor pressure. By using lithium molten salt as the electrolyte, a highly safe lithium secondary battery can be provided. Furthermore, alkali metal molten salts that do not produce concentration polarization can achieve a 100% transport rate when used in batteries.

[0004] However, because alkali metal salts have high melting points, batteries were limited to use at high temperatures where the alkali metal salts were in a liquid state (molten salt, ionic liquid).

[0005] Japanese Patent Publication No. 2014-165110 discloses a lithium secondary battery that operates from room temperature to over 100°C by using a mixed salt of Li[(FSO2)(CF3SO2)N] and Li[(FSO2)2N].

[0006] International Publication No. 2020 / 146274 discloses (fluorosulfonyl)sulfonylamide potassium salt (KMPSA), an asymmetric salt having an ether side chain on the opposite side of the fluoro group from the nitrogen atom. It is stated that KMPSA is being considered for application in potassium batteries due to its high solubility in solvents.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0008] An embodiment of the present invention aims to provide an alkali metal salt having a low melting point, a molten salt having a low melting point, and a secondary battery having an alkali metal salt having a low melting point. Here, "low melting point" means that the melting point measured by differential scanning calorimetry is 130°C or lower.

Means for Solving the Problems

[0009] The present invention includes the following aspects. [1] An alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group with a nitrogen atom in between. [2] The alkali metal salt according to [1], represented by the following formula (1).

Chemical Formula

Chemical Formula

[10] A supercooled salt, the molten salt described in [9].

[11] A secondary battery having an electrolyte containing an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group with a nitrogen atom in between.

[12] An electrolyte comprising an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group with a nitrogen atom in between, and substantially free of organic solvents.

[13] A secondary battery having an electrolyte that is substantially free of organic solvents, comprising an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group with a nitrogen atom in between.

[14] Alkali metal salts in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or fluorosulfonyl group, with a nitrogen atom in between.

[15] The alkali metal salt described in

[14] , represented by the following formula (1). [ka] [In formula (1), R 1 R is a trifluoromethylsulfonyl group or a fluorosulfonyl group, 2 [-CH2-CH2-O-] is a linear organic group having two [-CH2-CH2-O-] groups, and M is an alkali metal.

[16] The alkali metal salts described in

[14] or

[15] , represented by (Chemical Formula 1), (Chemical Formula 2), (Chemical Formula 3), (Chemical Formula 4), or (Chemical Formula 5) below. In (Chemical Formula 1), (Chemical Formula 2), (Chemical Formula 3), (Chemical Formula 4), or (Chemical Formula 5) below, M is an alkali metal. [ka]

[17] The alkali metal salt is a lithium salt, as described in any one of

[14] to

[16] .

[18] A molten salt comprising an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or a fluorosulfonyl group with a nitrogen atom in between.

[19] The molten salt according to

[18] , comprising an alkali metal salt represented by the following formula (1). [ka] [In formula (1), R 1 R is a trifluoromethylsulfonyl group or a fluorosulfonyl group, 2 [-CH2-CH2-O-] is a linear organic group having two [-CH2-CH2-O-] groups, and M is an alkali metal.

[20] The alkali metal salt is a molten salt according to

[18] or

[19] , represented by the following (Chemical Formula 1), (Chemical Formula 2), (Chemical Formula 3), (Chemical Formula 4), or (Chemical Formula 5). In the following (Chemical Formula 1), (Chemical Formula 2), (Chemical Formula 3), (Chemical Formula 4), or (Chemical Formula 5), ​​M is an alkali metal. [ka]

[21] The alkali metal salt is a lithium salt, the molten salt according to any one of

[18] to

[20] .

[22] A mixed salt of a first molten salt, which is the molten salt, and a second molten salt having a different structure from the first molten salt, wherein the melting point of the second molten salt is lower than the melting point of the first molten salt and the melting point of the second molten salt, as described in any one of

[18] to

[22] .

[23] The molten salt described in

[22] , which is a supercooled salt.

[24] A secondary battery having an electrolyte containing an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or a fluorosulfonyl group with a nitrogen atom in between.

[25] An electrolyte comprising an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or a fluorosulfonyl group with a nitrogen atom in between, and substantially free of organic solvents.

[26] A secondary battery having an electrolyte that is substantially free of organic solvents, comprising an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or a fluorosulfonyl group with a nitrogen atom in between. [Effects of the Invention]

[0010] According to embodiments of the present invention, a low-melting-point alkali metal salt, a low-melting-point molten salt, and a secondary battery having a low-melting-point alkali metal salt can be provided. [Brief explanation of the drawing]

[0011] [Figure 1]This is a cross-sectional view illustrating the structure of a secondary battery according to an embodiment. [Figure 2] This is a table showing the melting points of various alkali metal salts. [Figure 3] This figure shows the diffusion coefficients of various alkali metal salts. [Figure 4] This table shows the diffusion coefficients of various alkali metal salts at 140°C. [Figure 5] This figure shows the electrical conductivity of various alkali metal salts. [Figure 6] This figure shows an example of the decrease in the melting point of a mixed salt. [Figure 7] This figure shows the ionic conductivity of various alkali metal salts. [Figure 8] This figure shows the diffusion coefficients of various alkali metal salts. [Figure 9] This table shows the diffusion coefficients of various alkali metal salts. [Figure 10] This table shows the ionic conductivity of various alkali metal salts. [Figure 11] This table shows the ionic conductivity of various alkali metal salts. [Figure 12] This table shows the structure and thermophysical properties of each alkali metal salt. [Figure 13] This table shows the thermophysical properties of various alkali metal salts. [Modes for carrying out the invention]

[0012] <Secondary battery> Figure 1 shows an example of a secondary battery according to this embodiment. The secondary battery 1 of this embodiment shown in Figure 1 (hereinafter referred to as "battery 1") is a coin-type lithium-ion secondary battery. Battery 1 comprises a positive electrode 11, a negative electrode (anode) 12, and a separator 13 containing an electrolyte 14.

[0013] In the coin-type battery 1, the positive electrode 11 and the negative electrode 12 are stacked with a separator 13 in between, and sealed in a coin cell case 15. A spring 16 is placed on top of the negative electrode 12, and the coin cell case 15 is sealed with a lid 17. A gasket 18 is interposed on the side wall of the coin cell case 15.

[0014] The positive electrode 11, which absorbs and releases lithium ions, contains, for example, lithium cobalt oxide. The negative electrode 12, which absorbs and releases lithium ions, contains, for example, a carbon material. The separator 13, which is porous or the like, is made of, for example, polyolefin.

[0015] The electrolyte 14, as described later, is a molten salt containing an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or fluorosulfonyl group, with a nitrogen atom in between. Because the above molten salt has a low melting point, it is flame-retardant, and battery 1 is highly safe. Furthermore, because the above alkali metal salt has a low melting point (MP), battery 1 can be used at lower temperatures than conventional batteries using molten salts. In addition, because the above molten salt has a low melting point, its electron conductivity is improved, so battery 1 using the above molten salt as the electrolyte has, for example, excellent charge-discharge efficiency and charge-discharge characteristics (rate characteristics) at high currents.

[0016] Battery 1 is not limited to coin-type batteries, but may have various known structures, such as wound-type or laminate-type batteries. Battery 1 may have multiple unit cells (positive electrode / electrolyte / negative electrode), or it may have multiple units consisting of multiple unit cells. Battery 1 may also be a bipolar battery in which the positive and negative electrodes of adjacent unit cells share a common current collector.

[0017] Battery 1 is not limited to lithium-ion batteries; for example, it may be a lithium polymer battery, lithium sulfur battery, metallic lithium battery, sodium battery, or potassium battery.

[0018] <Alkali metal salts> One aspect of the present invention is an alkali metal salt in which two or more ether chains are arranged in series on opposite sides of a nitrogen atom from a trifluoromethylsulfonyl group (CF3SO2 group) or a fluorosulfonyl group (F(SO2) group). In lithium-ion batteries, electrolytes in which lithium metal salts are dissolved in organic solvents are widely used.

[0019] Known lithium metal salts include (salt A) Li[FTA]: fluorosulfonyl (trifluoromethylsulfonyl) amide lithium salt and (salt B) Li[FSA]: lithium bis(fluorosulfonyl) amide salt, as shown in Figure 2. Those skilled in the art may also refer to amide salts as imide salts. For example, Li[FTA] is also called Li[FTI]: fluorosulfonyl (trifluoromethylsulfonyl) imide lithium salt. Li[FTA] and Li[FTI] refer to the same lithium salt.

[0020] As explained in the background technology section, the melting point of the lithium salt Li[TfN3O1], obtained by substituting the potassium with lithium in a potassium salt having one ether chain on the opposite side of the trifluoromethylsulfonyl group with a nitrogen atom, was 256°C (Figure 2: Salt C). Similarly, the melting point of the lithium salt Li[TfN2O2], which also has one ether chain on the opposite side of the trifluoromethylsulfonyl group with a nitrogen atom, was over 150°C (Figure 2: Salt D). Note that the terminal end of salt D, whose melting point was measured, is an ethyl group, unlike salts C, E, X, and Y, which have methyl groups at their ends.

[0021] In contrast, the melting point of the lithium salt (Figure 2, salt E) having three ether chains on the opposite side of the trifluoromethylsulfonyl group with a nitrogen atom was 131°C. The melting point of the potassium salt (Figure 2, salt F) having a long alkyl group side chain on the opposite side of the trifluoromethylsulfonyl group with a nitrogen atom was over 180°C. Although not shown in the figure, the melting point of the lithium salt having four ether chains on the opposite side of the trifluoromethylsulfonyl group with a nitrogen atom was 180°C.

[0022] From the differences in the melting points of the above-mentioned plurality of alkali metal salts, it was found that the ether side chain contributes to the decrease in melting point because it is more flexible than the alkyl side chain. However, a side chain that is too long may contribute to an increase in the melting point of the salt due to an increase in molecular weight.

[0023] Note that even in the case of a salt having a flexible side chain in which two or more ether chains are arranged in series on the opposite side of the trifluoromethylsulfonyl group with a nitrogen atom intervening (strictly speaking, two oxygen atoms are arranged in series as an ether chain), if the side chain has many ether groups or ethylene groups, there is a possibility that the melting point will increase. Therefore, the flexible side chain preferably has a methyl group or an ethyl group at the terminal and has two or three ethylene groups.

[0024] In one aspect of the present invention, the alkali metal salt is preferably an alkali metal salt represented by the following formula (1).

[0025]

Chemical formula

[0026] In formula (1), R 1 is a trifluoromethylsulfonyl group or a fluorosulfonyl group (F(SO2) group). In formula (1), R 2 is a linear organic group having two [-CH2-CH2-O-]. In formula (1), M is an alkali metal. M is, for example, Li, Na or K.

[0027] In one aspect of the present invention, the alkali metal salt is preferably an alkali metal salt represented by the following formula (1)-1.

[0028]

Chemical formula

[0029] In formula (1)-1, R1 This is a trifluoromethylsulfonyl group or a fluorosulfonyl group (F(SO2) group). In equation (1)-1, n is either 0 or 1. In formula (1)-1, R 3 This is either a methyl group or an ethyl group. In formula (1)-1, M is an alkali metal. M is, for example, Li, Na, or K. M is preferably Li.

[0030] In one embodiment of the present invention, the alkali metal salt is preferably an alkali metal salt represented by the following formula (1)-1-1 or formula (1)-1-2.

[0031] [ka]

[0032] In formula (1)-1-1, formula (1)-1-2, M, n, R 3 The explanation for this is the same as the explanation in equation (1)-1.

[0033] In one embodiment of the present invention, the alkali metal salt is preferably a metal salt represented by the following (Chemical Formula 1), (Chemical Formula 2), (Chemical Formula 3), (Chemical Formula 4), or (Chemical Formula 5). In the following (Chemical Formula 1), (Chemical Formula 2), (Chemical Formula 3), (Chemical Formula 4), or (Chemical Formula 5), ​​M is an alkali metal.

[0034] [ka]

[0035] In one aspect of the present invention, specific examples of preferred alkali metal salts are shown below.

[0036] [ka]

[0037] [ka]

[0038] [ka]

[0039] [ka]

[0040] [ka]

[0041] Method for producing alkali metal salts The alkali metal salt of the present invention can be produced by the following production method 1 or production method 2.

[0042] [ka]

[0043] [ka]

[0044] The alkali metal salt of the present invention can be produced by the following production method 3 or production method 4.

[0045] [ka]

[0046] [ka]

[0047] In the above manufacturing methods 1 and 3, sodium salts can be produced by using NaH, NaOH, or Na2CO3 instead of lithium salt (LiH).

[0048] The alkali metal salt of the present invention can be produced by the following production method 5.

[0049] [ka]

[0050] <molten salt> One aspect of the present invention is a molten salt comprising an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group with a nitrogen atom in between. The description of the alkali metal salt contained in the molten salt is the same as the description of the alkali metal salt in the present invention.

[0051] By using a molten salt instead of a liquid electrolyte as the electrolyte, improvements in battery safety and charge / discharge efficiency are expected. For this reason, there has been a demand for molten salts with a low melting point Tm, which is below the battery's operating temperature (e.g., 25°C).

[0052] It is known that the melting point of a mixed salt, which is a mixture of several different alkali metal salts, can decrease significantly depending on the mixing ratio. For example, as shown in Figure 6, in a mixed salt of salt A:Li[FTA] and salt B:Li[FSA], there are mixing ratios in which the melting point is lower than that of Li[FTA] (101.3°C) and Li[FSA] (140.5°C).

[0053] The melting point of a mixed salt decreases as the individual melting points of the alkali metal salts being mixed decrease. Therefore, low-melting-point alkali metal salts have been sought after.

[0054] Here, the melting point of alkali metal molten salts can decrease when multiple salts are mixed. For example, Figure 6 shows the change in melting point of a mixed salt obtained by mixing salt A and salt B with respect to the mixing ratio.

[0055] Since salts X and Y have lower melting points than salt B (Li[FSA]), when mixed with salt A (Li[FTA]), a lower melting point is expected compared to the mixed salt of salt A and salt B shown in Figure 6. The salts mixed with salts X and Y are not limited to salt A; various known lithium salts may be used, or salt X and salt Y may be mixed. Furthermore, three or more types of salts may be mixed. The mixing ratio of multiple salts can be selected as appropriate.

[0056] In other words, one aspect of the present invention is a mixed salt of a first molten salt (salt X or salt Y) which is the alkali metal salt of the present invention, and a second molten salt having a different structure from the first molten salt, wherein the molten salt has a lower melting point than the melting point of the first alkali metal and the melting point of the second alkali metal salt.

[0057] Furthermore, even if the mixed salt has a melting point above room temperature, if it is a deeply supercooled salt that remains liquid at room temperature, it can be preferably used as the electrolyte for battery 1. Supercooling refers to a phase transition in which a substance remains liquid even below its melting point. A supercooled molten salt will solidify over time. Once a molten salt solidifies, its electrical conductivity decreases rapidly. However, a solidified molten salt can be heated above its melting point to become liquid again, and then re-enter the supercooled state when the temperature drops below its melting point.

[0058] In the case of supercooled molten salts, to lower the glass transition temperature (Tg), one or more organic polymers having polar functional groups of N, O, and F that coordinate to the alkali metal salt cations may be included in an amount of 5 mol% to 50 mol%. Examples of organic polymers are shown below.

[0059] Polypropylene glycol (PPG): Mn=2000 Polyethylene glycol (PEG, PEO): Mn = 35000 Polymethyl methacrylate (PMMA): Mn=48000

[0060] Furthermore, the molten salt in the embodiment may contain a small amount of organic solvent to reduce viscosity.

[0061] <Electrolyte> One aspect of the present invention is an electrolyte that contains an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group with a nitrogen atom in between, and which is substantially free of organic solvents. Here, "substantially free of organic solvents" means that the organic solvent content is 5% by mass or less relative to the total volume of the electrolyte.

[0062] One aspect of the present invention is a secondary battery having an electrolyte that is substantially free of organic solvents, comprising an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group with a nitrogen atom in between. Here, "substantially free of organic solvents" means that the organic solvent content is 5% by mass or less relative to the total amount of electrolytes.

[0063] The present invention is not limited to the embodiments described above. The present invention can be modified, altered, or combined in various ways, as long as the spirit of the invention is not altered. [Examples]

[0064] The present invention will be described in more detail in the following examples, but the present invention is not limited in any way by these examples.

[0065] <Example 1> As a low-melting-point metal salt, the lithium salt X:Li[TfN2O2O1] shown in Figure 2 was synthesized by the following method.

[0066] 2-(2-methoxyethoxy)ethaneamine (10.12 g, 85 mmol, 1.00 equivalent) and triethylamine (18.0 mL, 13.11 g, 133 mmol, 1.52 equivalents) were dissolved in 180 mL of dry water and stirred at -78°C using a dry ice bath under Schlenk conditions. Next, a solution of trifluoromethanesulfonic acid anhydride (15.7 mL, 26.39 g, 94 mmol, 1.10 equivalents) dissolved in 80 mL of dry dichloromethane was added dropwise at a rate of approximately 1.5 mL / min. After the dropwise addition was complete, the reaction mixture was heated to room temperature and stirred for 5 hours. Dichloromethane was removed using a rotary evaporator to obtain a colorless, transparent liquid. 35 mL of 4M NaOH aqueous solution was added to this residue, and the mixture was washed three times with 40 mL of dichloromethane. Next, 40 mL of 6 M aqueous HCl was added, and the aqueous layer was extracted three times with 40 mL of dichloromethane. The combined organic layer was dried over MgSO4, and the solvent was removed under reduced pressure using a rotary evaporator. 10.5 g of a colorless, transparent liquid was obtained by vacuum distillation (oil bath temperature: approximately 48°C, 0.04 mbar). NMR measurement confirmed that 2-(2-methoxyethoxy)ethyl((trifluoromethyl)sulfonyl)amide (H[TfN2O2O1]) (42.0 mmol, isolation yield 49%) was obtained.

[0067] 1 H NMR (DMSO-d6, 500 MHz, δ in ppm): 9.46 (s, 1H, NH), 3.54-3.43 (m, 6H, CH2-O-C2H4-O), 3.27 (t, 3 J H / H = 10.9 Hz, 2H, N-CH2), 3.24 (s, 3H, CH3). 13 C{ 1 H} NMR (DMSO-d6, 126 MHz, δ in ppm): 120.15 (q, 1 J C / F = 322.3 Hz, CF3), 71.71 (s, N- CH2), 70.01 (s, N-CH2-CH2), 69.52 (s, N-C2H4-O-C2H4), 58.44 (s, N-C2H4- O-C2H4), 43.71 (s, CH3). 19 F NMR (DMSO-d6, 471 MHz, δ in ppm): -77.42 (s, CF3).

[0068] Lithium hydride (0.141 g, 18 mmol, 1.50 equivalents) was suspended in 50 mL of dry acetonitrile in a 100 mL Schlenk flask. To this suspension, 2.81 g (11 mmol, 1.00 equivalent) of 2-(2-methoxyethoxy)ethyl((trifluoromethyl)sulfonyl)amide was slowly added in an ice bath. After the addition was complete, the mixture was stirred for 1.5 hours and then filtered into another Schlenk flask using a filter cannula (glass fiber filter paper, Teflon® tape, and PTFE cannula). The solvent was removed to obtain a solid product, which was dried under reduced pressure at 50°C to obtain 2.54 g (9.86 mmol, isolation yield 88%) of lithium(2-(2-methoxyethoxy)ethyl)((trifluoromethyl)sulfonyl)amide (Li[TfN2O2O1]).

[0069] 1 H NMR (DMSO-d6, 500 MHz, δ in ppm): 3.46-3.38 (m, 4H, CH2-O-CH2), 3.27 (t, 3 J H / H = 14.32 Hz, 2H, CH2-CH2-O), 3.22 (s, 3H, CH3), 2.97 (t, 3 J H / H (= 14.89 Hz, 2H, N-CH2). 13 C{ 1 H} NMR (DMSO-d6, 126 MHz, δ in ppm): 123.42 (q, 1 J C / F = 334.8 Hz, CF3), 73.54 (s, N- CH2), 71.87 (s, N-CH2-CH2), 69.87 (s, N-C2H4-O-C2H4), 58.57 (s, N-C2H4- O-C2H4), 46.04 (s, CH3). 19 F NMR (DMSO-d6, 471 MHz, δ in ppm): -75.69 (s, CF3). ESI-MS (negative ion mode): m / z calculated for [TfN2O2O1] -= 250.21; found = 250.14.

[0070] Lithium salt X has a flexible side chain in which two or more ether chains are arranged in series on the opposite side of the trifluoromethylsulfonyl group, with a nitrogen atom in between. Hydrocarbon chains were inserted between the multiple ether chains. The melting point of salt X was 98.3°C, and the decomposition temperature of salt X was 250°C or higher.

[0071] The melting point and decomposition temperature were measured by the following method. [Measurement of thermal decomposition temperature (TGA)] Thermogravimetric analysis was performed using STA7200 (Hitachi High-Tech Science). During measurement, the sample chamber was purged with nitrogen (100 mL / min). The TGA open pan (aluminum, outer diameter 5.2 mm, height 2.5 mm, volume 45 μL, upper temperature limit 600 °C, Hitachi High-Tech Science) was handled with PVDF coated tweezers (ideal-Tek). The sample was filled into the pan in a dry chamber and heated at a rate of 5 °C / min over a temperature range of 30 °C to 550 °C. The temperature at which the weight loss reached 5% was defined as the decomposition temperature (T). d ) [Melting point measurement (DSC)] Measurements were performed using a DSC7020 (Hitachi High-Tech Science). The sample was sealed in an aluminum pan (3 MPa, outer diameter 6 mm, height 4 mm, volume 15 μL, Hitachi High-Tech Science) in an Ar-atmosphere glove box. To erase the thermal history, the pan containing the sample was heated to 80°C, then cooled to -100°C, and finally cooled to 10°C min. -1 The temperature was raised to 200°C at this heating rate. The final heating process was used for the analysis. The melting point (T) of the sample m ) was read from the onset of the endothermic peak.

[0072] <Example 2> As a low-melting-point metal salt, the lithium salt Y:Li[PMEA] shown in Figure 2 was synthesized by the following method.

[0073] Li[PMEA] was prepared using the same method as that used for the synthesis of Li[TfN2O2O1]. Lithium hydride (0.20 g, 18 mmol, 1.48 equivalents) was reacted with (3-(2-methoxyethoxy)propyl)((trifluoromethyl)sulfonyl)amide (4.5 g, 17 mmol, 1.00 equivalent). This reaction yielded 3.7 g (13 mmol, isolation yield 80%) of lithium (3-(2-methoxyethoxy)propyl)((trifluoromethyl)sulfonyl)amide (Li[PMEA]).

[0074] 1 H NMR (DMSO-d6, 500 MHz, δ in ppm): 3.43-3.35 (m, 6H, CH2-O-C2H4), 3.22 (s, 3H, CH3), 2.87 (t, 3 J H / H = 13.17 Hz, 2H, N-CH2), 1.50 (quint, 3 J H / H (= 26.92 Hz, 2H, N-CH2-CH2). 13 C{ 1 H} NMR (DMSO-d6, 126 MHz, δ in ppm): 123.91 (q, 1 J C / F 33.70 (s, CH3). 19 F NMR (DMSO-d6, 471 MHz, δ in ppm): -75.50 (s, CF3). ESI-MS (negative ion mode): m / z calculated for [TfN3O2O1] - = 264.24; found = 264.17.

[0075] Lithium salt Y has a flexible side chain in which two or more ether chains are arranged in series on the opposite side of the trifluoromethylsulfonyl group, with a nitrogen atom in between. Hydrocarbon chains were inserted between the multiple ether chains. The melting point of salt Y was 114.6°C, and the decomposition temperature of salt Y was above 250°C.

[0076] <Comparative Example 1>

[0077] As Comparative Example 1, (Salt A)Li[FTA]:fluorosulfonyl(trifluoromethylsulfonyl)amide lithium salt, shown in Figure 2, was used. Hereafter, it may be referred to as "Lithium Salt A". Lithium salt A is (fluorosulfonyl)(trifluoromethanesulfonyl)imide=lithium or lithium(fluorosulfonyl)(trifluoromethanesulfonyl)imide manufactured by Fujifilm Wako Pure Chemical Industries, Ltd. I used it.

[0078] Figure 3 shows the temperature dependence of the diffusion coefficient D for comparative example A:Li[FTA], lithium salt X:Li[TfN2O2O1], and lithium salt Y:Li[PMEA], lithium salt from example 2. Figure 4 is a table showing the diffusion coefficient D of the above salts at 140°C.

[0079] The diffusion coefficient D was measured using a nuclear magnetic resonance spectrometer (JEOL, ECX400) by a known pulsed magnetic field gradient NMR method employing a magnetic field gradient and spin echo method. Specifically, the change in echo signal intensity was determined by varying the magnetic field gradient strength, and the diffusion coefficient D was calculated according to the Stejskal-Tanner equation.

[0080] It was confirmed that lithium salt X:Li[TfN2O2O1] (Example 1) and lithium salt Y:Li[PMEA] (Example 2) have larger diffusion coefficients than lithium salt A:Li[FTA] (Comparative Example 1).

[0081] Figure 5 shows the temperature dependence of the conductivity σ of lithium salt A:Li[FTA] (Comparative Example 1), lithium salt X:Li[TfN2O2O1] (Example 1), and lithium salt Y:Li[PMEA] (Example 2).

[0082] The conductivity σ was measured using the complex impedance method with a measuring instrument (VMP2, Biologic). The measurement was performed with a frequency range of 500 kHz to 1 Hz and an applied voltage of 10 mV. Molten salt was introduced into a stainless steel electrode bielectrode cell (manufactured by Miclab) in a glove box, and the conductivity σ was measured. The cell constant of the stainless steel electrode bielectrode cell had been calculated using a standard hydrochloric acid solution prior to the measurement.

[0083] It was confirmed that lithium salt X:Li[TfN2O2O1], which is Example 1, has higher conductivity than lithium salt A:Li[FTA], which is Comparative Example 1.

[0084] <Example 3> As a low-melting-point metal salt, the lithium salt Z:Li[TfN2O2O2] shown below was synthesized by the following method.

[0085] Li[TfN2O2O2] was prepared using the same method as that used for the synthesis of Li[TfN2O2O1]. Lithium hydride (0.319 g, 40 mmol, 1.50 equivalents) was suspended in 40 mL of dry acetonitrile in a 100 mL Schlenk flask. To this suspension, 7.00 g (26 mmol, 1.00 equivalent) of 2-(2-ethoxyethoxy)ethyl((trifluoromethyl)sulfonyl)amide was slowly added in an ice bath. After the addition was complete, the mixture was stirred for 2 hours and then filtered into another Schlenk flask using a filter cannula (glass fiber filter paper, Teflon® tape, and PTFE cannula). The solvent was removed by distillation to obtain a solid product, which was then dried under reduced pressure at 60°C to obtain 2.18 g (8.04 mmol, isolation yield 30%) of lithium (2-(2-ethoxyethoxy)ethyl)((trifluoromethyl)sulfonyl)amide (Li[TfN2O2O2]).

[0086] 1 H NMR (DMSO-d6, 500 MHz, δ in ppm): 3.46-3.25 (m, 8H, C2H4-O-C2H4-O), 3.27 (q, 3 J H / H = 14.7 Hz, 2H, CH2-CH3), 1.08 (t, 3 J H / H (= 13.7 Hz, 3H, CH3). 13 C{ 1 H} NMR (DMSO-d6, 126 MHz, δ in ppm): 120.15 (q, 1 J C / F = 322.6 Hz, CF3), 73.64 (s, N- CH2), 70.13 (s, N-CH2-CH2), 69.82 (s, N-C2H4-O-C2H4), 66.05(s, N-C2H4- O-C2H4), 46.05 (s, CH2-CH3), 15.66 (s, CH3). 19 F NMR (DMSO-d6, 471 MHz, δ in ppm): -75.69 (s, CF3).

[0087] [ka]

[0088] <Example 4> As a low-melting-point metal salt, the lithium salt F:Li[FN2O2O1] shown below was synthesized by the following method.

[0089] 1-(fluorosulfonyl)-2,3-dimethyl-1H-imidazolium trifluoromethanesulfonate (5.07 g, 15.5 mmol, 1.00 equivalent), 60 mL of dry acetonitrile, and 2-(2-methoxyethoxy)ethylamine (1.73 g, 14.5 mmol, 0.94 equivalents) were added to a round-bottom flask and stirred at room temperature for 2.5 hours. The solvent was then removed. 30 mL of water was added, and the mixture was extracted twice with 40 mL of ethyl acetate. The mixture was washed with saturated saline solution, and the solvent was removed using a rotary evaporator. The resulting residue was dried at room temperature under reduced pressure to obtain 3.071 g of H[FN2O2O1] (15.3 mmol, isolation yield 99%).

[0090] 1 H NMR (DMSO-d6, 500 MHz, δ in ppm): 9.46 (s, 1H, NH), 3.54-3.43 (m, 8H, CH2-O-C2H4-O), 3.24 (s, 3H, CH3). 13 C{ 1 H} NMR (DMSO-d6, 126 MHz, δ in ppm): 71.70 (s, N- CH2), 70.03 (s, N-CH2-CH2), 68.86 (s, N-C2H4-O-C2H4), 58.55 (s, N-C2H4- O-C2H4), 43.93 (s, CH3). 19 F NMR (DMSO-d6, 471 MHz, δ in ppm): 52.01 (s, SF).

[0091] Lithium hydroxide monohydrate (0.12 g, 4.92 mmol, 0.97 equivalents), 10 mL of water, and H[FN2O2O1] (1.02 g, 5.07 mmol, 1.00 equivalent) were added to a 50 mL Schlenk flask and stirred at room temperature under an Ar atmosphere for 5 hours. The solvent was removed by vacuum drying, and the mixture was washed several times with dry dichloromethane and vacuum dried for 1 day to obtain 0.74 g of Li[FN2O2O1] (3.69 mmol, isolation yield 71%).

[0092] 1H NMR (DMSO-d6, 500 MHz, δ in ppm): 3.59-3.42 (m, 6H, CH2-O-C2H4-O), 3.23 (s, 3H, CH3), 3.09 (t, 3 J H / H (= 11.45 Hz, 2H, N-CH2). 13 C{ 1 H} NMR (DMSO-d6, 126 MHz, δ in ppm): 71.67 (s, N- CH2), 69.99 (s, N-CH2-CH2), 67.24 (s, N-C2H4-O-C2H4), 58.60 (s, N-C2H4- O-C2H4), 44.15 (s, CH3). 19 F NMR (DMSO-d6, 471 MHz, δ in ppm): 52.09 (s, SF).

[0093] [ka]

[0094] Figure 7 shows the temperature dependence of the ionic conductivity σ for lithium salt A:Li[FTA] (Comparative Example 1), lithium salt X:Li[TfN2O2O1] (Example 1), lithium salt Y:Li[PMEA] (Example 2), and lithium salt Z:Li[TfN2O2O2] (Example 3).

[0095] The ionic conductivity σ was measured using the complex impedance method with a measuring instrument (VMP2, Biologic). The measurement was performed with a frequency range of 500 kHz to 1 Hz and an applied voltage of 10 mV. Molten salt was introduced into a stainless steel electrode bielectrode cell (manufactured by Miclab) in a glove box, and the conductivity σ was measured. The cell constant of the stainless steel electrode bielectrode cell had been calculated using a standard hydrochloric acid solution prior to the measurement.

[0096] It was confirmed that lithium salt X:Li[TfN2O2O1] (Example 1), lithium salt Y:Li[PMEA] (Example 2), and lithium salt Z:Li[TfN2O2O2] (Example 3) have a higher ionic conductivity σ than lithium salt A:Li[FTA] (Comparative Example 1).

[0097] Figure 8 shows the temperature dependence of the diffusion coefficient D for comparative example A:Li[FTA], lithium salt X:Li[TfN2O2O1], and lithium salt Y:Li[PMEA], lithium salt example 2. Figure 8 is a table showing the diffusion coefficient D of the above salts at 140°C.

[0098] The diffusion coefficient D was measured using a nuclear magnetic resonance spectrometer (JEOL, ECX400) by a known pulsed magnetic field gradient NMR method employing a magnetic field gradient and spin echo method. Specifically, the change in echo signal intensity was determined by varying the magnetic field gradient strength, and the diffusion coefficient D was calculated according to the Stejskal-Tanner equation.

[0099] It was confirmed that lithium salts X:Li[TfN2O2O1] (Example 1), Y:Li[PMEA] (Example 2), and Z:Li[TfN2O2O2] (Example 3) have larger diffusion coefficients than lithium salt A:Li[FTA] (Comparative Example 1).

[0100] Figure 9 shows the values ​​of the diffusion coefficient D for comparative example A:Li[FTA], lithium salt X:Li[TfN2O2O1], and lithium salt Y:Li[PMEA], lithium salt example 2. Figures 10 and 11 show the ionic conductivity σ values ​​for comparative example 1, lithium salt A:Li[FTA], example 1, lithium salt X:Li[TfN2O2O1], and example 2, lithium salt Y:Li[PMEA]. Figure 12 shows the structure and thermophysical properties of each alkali metal salt.

[0101] Figure 13 shows the measured decomposition temperature (TGA) results for lithium salt X:Li[TfN2O2O1] (Example 1), lithium salt Y:Li[PMEA] (Example 2), and lithium salt Z:Li[TfN2O2O2] (Example 3).

Claims

1. An alkali metal salt in which two or more ether chains are arranged in series on the opposite side of the trifluoromethylsulfonyl group, with a nitrogen atom in between.

2. The alkali metal salt according to claim 1, represented by the following formula (1). 【Chemistry 1】 [In formula (1), R １ R is a trifluoromethylsulfonyl group, ２ is [-CH ２ -CH ２ It is a linear organic group having two -O- groups, where M is an alkali metal.

3. The alkali metal salt according to claim 1 or 2, represented by (chemical formula 1) or (chemical formula 2) below. In the following chemical formulas (1) or (2), M is an alkali metal. 【Chemistry 2】

4. The alkali metal salt according to claim 1 or 2, wherein the alkali metal salt is a lithium salt.

5. A molten salt containing an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group, with a nitrogen atom in between.

6. The molten salt according to claim 5, comprising an alkali metal salt represented by the following formula (1). 【Transformation 3】 [In formula (1), R １ R is a trifluoromethylsulfonyl group, ２ is [-CH ２ -CH ２ It is a linear organic group having two -O- groups, where M is an alkali metal.

7. The molten salt according to claim 5 or 6, wherein the alkali metal salt is represented by (Chemical Formula 1) or (Chemical Formula 2) below. In the following chemical formulas (1) or (2), M is an alkali metal. 【Chemistry 4】

8. The molten salt according to claim 5 or 6, wherein the alkali metal salt is a lithium salt.

9. A mixed salt of a first molten salt, which is the molten salt, and a second molten salt having a different structure from the first molten salt, wherein the melting point is lower than that of the first molten salt and the second molten salt, according to claim 5 or 6.

10. The molten salt according to claim 9, which is a supercooled salt.

11. A secondary battery having an electrolyte containing an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group, with a nitrogen atom in between.

12. An electrolyte containing an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group, with a nitrogen atom in between, and substantially free of organic solvents.

13. A secondary battery having an electrolyte that is substantially free of organic solvents, comprising an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group with a nitrogen atom in between.

14. An alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or fluorosulfonyl group, with a nitrogen atom in between.

15. The alkali metal salt according to claim 14, represented by the following formula (1). 【Transformation 5】 [In formula (1), R １ is a trifluoromethylsulfonyl group or a fluorosulfonyl group, R ２ is a linear organic group having two [—CH ２ —CH ２ —O—], and M is an alkali metal.]

16. The alkali metal salt according to claim 14 or 15, represented by (Chemical Formula 1), (Chemical Formula 2), (Chemical Formula 3), (Chemical Formula 4), or (Chemical Formula 5) below. In the following chemical formulas (1), (2), (3), (4), or (5), M is an alkali metal. 【Transformation 6】

17. The alkali metal salt according to claim 14 or 15, wherein the alkali metal salt is a lithium salt.

18. A molten salt comprising an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or fluorosulfonyl group, with a nitrogen atom in between.

19. The molten salt according to claim 18, comprising an alkali metal salt represented by the following formula (1). 【Transformation 7】 [In formula (1), R １ R is a trifluoromethylsulfonyl group or a fluorosulfonyl group, ２ is [-CH ２ -CH ２ It is a linear organic group having two -O- groups, where M is an alkali metal.

20. The molten salt according to claim 18 or 19, wherein the alkali metal salt is represented by (Chemical Formula 1), (Chemical Formula 2), (Chemical Formula 3), (Chemical Formula 4), or (Chemical Formula 5) below. In the following chemical formulas (1), (2), (3), (4), or (5), M is an alkali metal. 【Transformation 8】

21. The molten salt according to claim 18 or 19, wherein the alkali metal salt is a lithium salt.

22. A mixed salt of a first molten salt, which is the molten salt, and a second molten salt having a different structure from the first molten salt, wherein the melting point is lower than that of the first molten salt and the second molten salt, according to claim 18 or 19.

23. The molten salt according to claim 22, which is a supercooled salt.

24. A secondary battery having an electrolyte containing an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or a fluorosulfonyl group, with a nitrogen atom in between.

25. An electrolyte that contains an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or fluorosulfonyl group, with a nitrogen atom in between, and is substantially free of organic solvents.

26. A secondary battery having an electrolyte that is substantially free of organic solvents, comprising an alkali metal salt in which two or more ether chains are arranged in series on the opposite side of a trifluoromethylsulfonyl group or a fluorosulfonyl group with a nitrogen atom in between.

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